I suppose the Jennifer of alternate-1985 lived a different life but it's hard to say since we don't see her.

@Strannger18 said:

Was Jennifer different in this world or was time traveling with Doc keeping her safe from the changed timeline?

Marty was in another country and would have the memories of himself. So maybe she has an alternate.

Well Doc had an alternate committed to an insane asylum, there was an alternate Marty in a boarding school in Switzerland so it stands to reason there was an alternative Jennifer running around somewhere! The Jennifer on the porch swing was the regular 1985 Jennifer passed out!